Children's secondhand smoke exposure (SHSe) remains a leading cause of avertible morbidity/mortality, with links to asthma, otitis, SIDS, behavior problems and risk of cancer and cardiovascular disease. Addressing SHSe is a public health priority, particularly in low-income, young children-a group with excess tobacco-related risk and burden. Community clinics (e.g., Women, Infants and Children [WIC]), can reach this population. WIC's standard practice for addressing SHSe includes minimal self-help advice to parents, an approach with inadequate efficacy. Clinical practice guidelines (AAR) recommend that practitioners Ask parents about child SHSe, Advise them about harms, and Refer smokers to intensive evidence-based treatments that address multiple determinants of smoking. Thus, we propose to test a multilevel, multimodal treatment model that combines a system-level WIC intervention following AAR guidelines with a more intensive, individual-level multimodal behavioral intervention (MBI) that integrates telephone SHSe reduction and cessation counseling with coaching on NCI's QuitPal mobile app and nicotine replacement therapy (NRT) use. We will train staff in Philadelphia WIC clinics to implement AAR with auto-fax referral to the trial. We will then randomize 372 eligible parents to receive AAR+MBI or AAR+CTL (attention control intervention). All participants will receive AAR because it is an easily adoptable, potentil standard of care in community clinics. The primary aim is to test the hypothesis that AAR+MBI compared to AAR+CTL will result in greater reductions in child cotinine (SHSe biomarker) and reported cigarettes exposed/day at 3-month end of treatment and 12-month follow-up. A secondary aim is to test the hypothesis that AAR+MBI vs. AAR+CTL will result in higher bioverified 7-day point prevalence quit rate among parents at 3- and 12-months. We will test the hypothesis that social support, urge coping skills, self-efficacy, and SHSe protective behaviors mediate effects of AAR+MBI on smoking outcomes and explore whether other residential smokers, level of nicotine dependence, depressive/anxious symptoms, weight concerns, intervention dosage, and pregnancy status moderate treatment effects. Our model balances necessary intervention intensity with feasible components (quitline, NRT, QuitPal) already available in under- served communities, thereby facilitating future dissemination. Unlike the NCI Quitline and many state services, the MBI follows best practice guidelines and does so without increasing clinic burden. It also can improve an underserved, high-risk population's access to and engagement in evidence-based treatment. This project has high impact potential: it will result in a novel, efficacious multilevel model for tackling the significant problem of child SHSe. Secondary aims results will inform science and theory by identifying how and for whom the model works. Future dismantling research can assess orthogonal and synergistic effects of intervention components.